Some conventional non-contact power supply systems have long induction lines. In such a non-contact power supply system, since voltage applied to an induction line is limited, the induction line is divided and each of the divided lines is connected to a power supply unit.
In such a non-contact power supply system, even when power supply units supply high-frequency currents at the same frequency to induction lines, a phase difference occurs between the high-frequency currents. When the pickup coil of a moving body is disposed across the induction lines having such a phase difference, electromotive force induced to the pickup coil is reduced. Further, when the phase difference reaches 180°, electromotive force induced to the pickup coil is generated in opposite directions, power feeding is disabled, and the outputs of two power supply units are short-circuited through the pickup coil, resulting in overcurrent or the like.
Thus, as is disclosed in Japanese Patent Laid-Open No. 3266088, waveforms of high-frequency currents fed to two induction lines are respectively detected and measured by a current transformer (CT), the phases of the high-frequency currents of the two induction lines are compared with each other to detect a phase difference therebetween in a PLL/VCO circuit, and a high-frequency current corrected according to the phase difference is supplied as a high-frequency current to one of the induction lines.
However, such a conventional non-contact power supply system requires a current transformer (CT) for a wide frequency domain in order to actually measure the waveforms of high-frequency currents and a PLL/VCO circuit for comparing the measured waveforms of the high-frequency currents of induction lines to detect a phase difference and performing synchronization, resulting in high cost. Further, phase differences may not be matched when the waveform of the high-frequency current of one of the induction lines cannot be measured.